1. Technical Field
This invention relates to colored microfine globular particles, a method for the production thereof, and uses thereof. More particularly, it relates to colored microfine globular particles which have carbon black uniformly dispersed therein and are usable as a toner for the development of images of electro static charge, as a filler for thermoplastic resin compositions and coating compositions, as a coating agent for thermosensitive transfer ink ribbons, as a coloring agent for thermosensitive transfer ink ribbons, as a coloring agent for thermosensitive transfer ink, thermosetting resin compositions, and backcoats in magnetic recording media, and as a charge control agent, a method for the production of the colored microfine globular particles, and uses of the colored microfine globular particles.
2. Background Art
The electrophotography is a process of producing an image by forming an electric latent image on a photosensitive element formed with a photoconductive material such as selenium, zinc oxide, or cadmium sulfide, developing the latent image with a developing powder, transferring the image of the developing powder as onto a sheet of paper, and fixing the transferred image on the paper.
Heretofore, the toner used for the development of images of electro static charge has been generally produced by melting and mixing for thorough dispersion a coloring agent and other additives (such as a charge control agent, an offset preventing agent, and a lubricant) in a thermoplastic resin, then finely crushing the resultant solid mixture, classifying the produced particles, and selecting those of desired particle diameters as colored microfine particles.
The method which produces the toner by the aforementioned crushing, however, possesses various drawbacks of its own. Firstly, it involves many steps of operation such as the step of producing a resin, the step of mixing the resin with a coloring agent and other additives, the step of crushing the resultant solid mixture, and the step of classifying the particles resulting from the crushing and obtaining particles of desired diameters as colored microfine particles and, necessitates use of various devices adapted to perform these steps. The toner produced by this method is very expensive as an inevitable consequence. Particularly for the purpose of obtaining a toner the particles of which have diameters falling in the range optimum for the production of an image clear and sparingly liable to fog, the step of classifying the particles constitutes itself an essential requirement. It is, however, difficult to obtain perfect removal of extremely fine particles and coarse particles by-produced during the step of crushing. Moreover, the by-produced rejectable particles raise a problem from the standpoint of yield. Secondly, it is extremely difficult to obtain uniform dispersion of the coloring agent and other additives in the resin during the step of mixing. Thirdly, since the particles of the toner produced by this method have no fixed shape and consequently possess no uniform triboelectric property, no uniform charging property is exhibited between the adjacent particles and, as the result, the resolution of the image obtained with the toner is inferior. Further, owing to the lack of uniform shape, the particles of the toner exhibit poor flowability and the extremely fine fragments produced when the particles are crushed during the course of triboelectrification induce the phenomenon of fogging of the developed image. Thus, the method under discussion is problematic in numerous ways.
For the purpose of eliminating the various drawbacks suffered by the toner produced by the crushing method, various methods have been proposed for the production of the toner by the emulsion polymerization or suspension polymerization technique (Japanese Patent Publication SHO 36(1961)-10,231, Japanese Patent Publication SHO 43(1968)-10,799, U.S. Pat. No. 3,959,153, and U.S. Pat. No. 3,634,251). These methods are meant to provide speedy synthesis of a toner containing carbon black, for example, as a coloring agent by the steps of adding the coloring agent and other additives to a polymerizable monomer and subjecting the resultant mixture to emulsion or suspension polymerization. These methods are capable of eliminating the drawbacks of the conventional crushing method to a considerably large extent. Since these methods involve absolutely no step of crushing, the particles produced thereby required no improvement in brittleness and these particles are globular in shape and therefore excellent in flowability and enjoy uniformity of triboelectric property.
The methods which rely on the technique of suspension polymerization for the production of a toner, however, possess a problem of their own. For example, the coloring matter, particularly carbon black, to be added is not uniformly dispersed and the uniform dispersion of the coloring agent aggravates the dispersion in the electric resistance and the triboelectricity of the toner particles. For the production of a toner capable of forming an image of excellent quality, therefore, these methods have room for further technical improvement.
Concerning this particular problem, as means of improving the dispersibility of carbon black in the polymerizing monomer, a method which consists in defining the kind of carbon black to be used (Japanese Patent Laid-Open SHO 56(1981)-106,250 and a method which comprises treating the carbon black with a coupling agent such as triethoxy silane (G.B. 1,583,564 or G.B. 1,583,411) have been proposed. These methods are not practicable because the dispersion of carbon black in the polymerizing monomer is not perfect and tends to increase the cost. There has also been proposed a method which resides in using a grafted carbon black obtained by polymerizing a monomer component in the presence of carbon black (DE 3,102,823). In this method, since the grafting ratio is low, the dispersion of the grafted carbon black in the polymerizing monomer is not obtained to a sufficient extent.
Where carbon black is added as a coloring agent and an electric charging agent for incorporation in a thermoplastic resin composition, a coating composition, a thermosensitive transfer ink ribbon coating agent, a thermosensitive transfer ink, a thermosetting resin composition, a back-coat of magnetic recording medium, or a charge control agent, the cohesive force generated between the particles of carbon black is so strong that it is extremely difficult for the carbon black to be uniformly mixed or dispersed under ordinary mixing or dispersing conditions.
An object of the present invention, therefore, is to provide novel colored microfine globular particles, a method for the production thereof, and uses thereof.
Another object of this invention is to provide colored microfine globular particles which have carbon black uniformly dispersed therein and are usable as a toner for the development of images of static charge, as a filler for thermoplastic resin compositions and coating compositions, as a coating agent for thermosensitive transfer ink ribbons, as a coloring agent for thermosensitive transfer ink, thermosetting resin compositions, and back-coats in magnetic recording media, and as a charge control agent, a method for the production of the colored microfine globular particles, and uses of the colored microfine globular particles.